1. Field of Invention
The present invention relates to a selective one-way screwdriver and, more particularly, to a selective one-way screwdriver with a torque arm perpendicular to the axis of a screwdriver bit so that a user can use a small force to generate a large torque.
2. Related Prior Art
A ratchet mechanism is used because it provides selective one-way driving so that a user will not drive while returning a tool to its original position, thus saving troubles in reengaging. Hence, ratchet mechanisms are used in various hand tools such as screwdrivers. Examples of such screwdrivers can be found in Taiwanese Patent Publication Nos. 500021, 507641, 527993 and 578653.
The ratchet mechanisms are used in the screwdrivers in order to provide selective one-way driving. However, as the bit and the handle extend in one axis, the torque arm is the radius of the handle. Hence, its operation is inconvenient and requires a large force. Limited by space, the replaceable bit can only be inserted in an extension rod of the handle. Without any device for retaining the bit, the bit often falls in operation, and this is inconvenient.
As discussed above, conventional ratchet screwdrivers do not provide adequate torque arms. Hence, their operation is inconvenient and requires a large force. In other words, there has not been any ratchet screwdriver that provides an adequate torque arm.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.